As shown in FIG. 4, an air bag assembly is disposed centrally on a vehicle steering wheel 10, which upon collision of a vehicle deploys and inflates an air bag. This air bag assembly includes a mounting plate, commonly referred to as a retainer. An inflator and an air bag are mounted to the mounting plate and covered by a modular cover 11. As shown in FIG. 5, the modular cover 11 has engaging portions 11a, 11b at its lateral sides to join spokes 12 of the steering wheel.
The modular cover 11 has tear lines 13 along which the modular cover can be ruptured when the air bag is deployed. The tear lines are in the form of a continuous groove or a semicontinuous groove. The tear lines may alternatively include spaced grooves of greater depth. When the cover has two different layers, i.e. a rigid layer and a soft layer, a slit may be formed in the rigid layer so that the cover may be ruptured along a predetermined line.
In the prior art modular cover 11, the tear lines 13 include tear lines 13a, 13b extending vertically along lateral sides of the cover 11, and a central tear line 13c extending centrally and laterally of the cover 11 as shown in FIGS. 4 and 5. A vertical direction is a direction from an occupant M toward a windshield G. A lateral direction is the width direction of a vehicle. In this case, the steering wheel is so oriented as to permit the vehicle to run on a straight line.
The tear lines 13a, 13b of the prior art modular cover 11 have ends P positioned substantially at the center of the engaging portions 11a, 11b of the modular cover 11 to join spokes 12. The modular cover 11 has portions S which extend from the ends P to the lower ends of the engaging portions 11a, 11b and remain unbroken when the cover 11 is ruptured. As a consequence, a flap (lower flap) of the modular cover 11 adjacent to the occupant is bent along a line P--P. A portion of the modular cover around the line P--P has a relatively high bending rigidity. This may prevent large bending of the lower flap.